1. Field of the Invention
The present invention relates to the improvement of a visual axis detection device which detects the rotation angle of the visual axis of the eye of a user who looks in the finder field, and detects the user's visual axis in accordance with the detected rotation angle.
2. Related Background Art
There have hitherto been proposed various devices which detect the positions that an observer observes on the plane of observation, the so-called visual axis (sight axis) detection devices (eye-cameras, for example).
In Japanese Patent Laid Open Application No. 1-274736, for example, the parallel luminous fluxes from a light source are projected on the anterior eye portion of an eye of the observer to obtain the visual axis by utilizing the corneal reflex images by the reflected light from the cornea, and the image formation positions in the pupil.
Also, Japanese Laid-Open Patent Application No. 4-242630 (corresponding to Japanese Patent Application No. 3-11492) has proposed an optical device provided with a visual axis detection function to execute various kinds of photography using a correction data gathering function (hereinafter referred to as calibration) for correcting the variations of visual axes between individual observers.
FIG. 25 illustrates the visual axis detection method. FIGS. 26A and 26B illustrate an eyeball image protected on the plane of an image sensor 14 in FIG. 25, and the output intensity obtained from the image sensor 14, respectively.
Now, in conjunction with FIG. 25, FIGS. 26A and 26B, the visual axis detection method will be described.
Each of the infrared light emitting diodes 13a and 13b is arranged substantially symmetrically in the direction X with respect to the optical axis s of a photodetecting lens 12 and divergently illuminates the eyeball of an observer (photographer), respectively.
The infrared light projected from the infrared light emitting diode 13b each of them illuminates the cornea 16 of the eyeball 15. At this juncture, a corneal reflex image d made by a part of the infrared light reflected on the surface of the cornea 16 is converged by the photodetecting lens 12, thus being reimaged at a position d' on an image sensor 14.
Likewise, the infrared light projected from the infrared light emitting diode 13a illuminates the cornea 16 of the eyeball 15. At this juncture, a corneal reflex image e made by a part of the infrared light reflected on the surface of the cornea 16 is converged by the photodetecting lens 12, thus being reimaged at a position e' on the image sensor 14.
Also, the luminous fluxes from the end portions a and b of the iris 17 form the images of the end portions a and b at the positions a' and b' on the image sensor 14 through the photodetecting lens 12. When the rotation angle .theta. of the optical axis t with respect to the optical axis s of the photodetecting lens 12 is small, and given the coordinate X of the end portions a and b of the iris 17 as xa and xb, the coordinate xc of the central position of the pupil 19 is expressed as follows: EQU xc.about.(xa+xb)/2
Also, given the coordinates X of the positions in which the corneal reflex images d' and e' are generated as xd' and xe'; the standard distance between the curvature center o of the cornea 16 and the center c of the pupil 19 as L.sub.oc, the coefficient with which to consider the individual variations of the distance L.sub.oc as A1, the rotation angle .theta. of the optical axis t of the eyeball 15 essentially satisfies the following relational equation because the coordinate X of the center points of the corneal reflex images d' and e' and the coordinate X xo of the curvature center o of the coordinate X agree with each other: EQU (A1*L.sub.oc)*sin.theta..congruent.xc-(xd+xe)/2 (1)
Therefore, it is possible to obtain the rotation angle .theta. of the optical axis t of the eyeball 15 by detecting the positions of each of the characteristic points (corneal reflex images d and e, and the end portions a and b of the iris 17) projected on a part of the image sensor 14 as shown in FIG. 26B in a visual axis operation processor. At this juncture, the above-mentioned equation (1) is rewritten as follows: EQU .beta.(A1*L.sub.oc)*sin.theta..congruent.(xa'+xb')/2-(xd'+xe')/2(2)
where .beta. is a magnification determined by the position of the eyeball 15 with respect to the photodetecting lens 12, and substantially, this is obtained as a function of the interval .vertline.xd'-xe'.vertline. of the corneal reflex images. The rotation angle .theta. of the optical axis t of the eyeball 15 is rewritten as follows: EQU .theta..congruent.ARCSIN{(xc'-xf')/.beta./(A1*L.sub.oc)} (3)
where EQU xc'.congruent.(xa'+xb')/2 EQU xf'.congruent.(xd'+xe')/2
Now, since the optical axis t of the eyeball 15 of the photographer and the visual axis do not agree, the visual axis .theta.H of the photographer in the horizonal direction is obtained by executing an angle correction .delta. between the visual axis and optical axis t when the rotation angle .theta. of the optical axis t in the horizontal direction has been obtained. Given the coefficient with which to consider the individual variations with respect to the angle correction .delta. between the optical axis t of the eyeball 15 and visual axis as B1, the visual axis of the photographer in the horizontal direction .theta.H is obtained as follows: EQU .theta.H=.theta..+-.(B1*.delta.) (4)
where the sign ".+-." is such that if the eye of the photographer who looks in the observation device is his left eye, the sign "+" is selected, and if it is his right eye, the sign "-" is selected provided that the rotation angle is positive when it rotates towards the right with respect to the photographer.
Also, in FIG. 26B, while an example in which the eyeball of the photographer rotates in the plane Z-X (horizontal plane, for example) is shown, it is possible to execute the same kind of detection when the eyeball of the photographer rotates in the plane X-Y (vertical plane, for example). However, since the component of the visual axis of the photographer in the vertical direction agrees with the component .theta.' of the optical axis t of the eyeball 15 in the vertical direction, the visual axis .theta.H in the vertical direction is: EQU .theta.V=.theta.'
Further, the positions (xn and yn) on the imaging plate in the finder field which the photographer looks in can be obtained as follows based upon the visual axis data .theta.H and .theta.V: EQU xn.congruent.m*.theta.H.congruent.m*[ARCSIN{(xc'-xf')/.beta./(A1*L.sub.oc)} .+-.(B*.alpha.)] (5) EQU yn.congruent.m.theta.V
where m is a constant which is determined by the finder optical systems of a camera.
Here, the coefficients A1 and B1 with which to correct the individual variations of the eyeball 15 of a photographer are obtained in such a manner that the photographer is requested to gaze at the visual targets arranged in given positions in the finder of a camera, and that the positions of the visual targets and the position of the gazing point calculated in accordance with the above-mentioned equation (5) are brought to agree with each other.
Usually, the operation to obtain the visual axis of a photographer and the point he looks at attentively is executed by the application of a software for the visual axis operation processor of a microcomputer.
Also, the coefficient with which to correct the individual variations of the visual axis usually corresponds to the rotation of the eyeball of a photographer in the horizontal direction. Thus, the two visual targets arranged in the finder of a camera are set in the horizontal direction with respect to the photographer.
The coefficient for the correction of the individual variations of the visual axis is obtained and, when the position on the imaging plate of the visual axis of the photographer who looks in the finder of a camera is calculated by using above equation (5), the visual axis information thus obtained will be utilized for the focus adjustment of a photographing lens, the exposure control, or the like.
As the gathering of the correction data for correcting errors due to the individual variations of the visual axis, that is, the calibration method, there has been proposed a method in which the visual axis data and pupil diameters of a photographer are collected at the time of the open aperture of a photographing lens and the minimum aperture thereof, that is, the diameters of the photgrapher's pupil eventually, because the ratio between the visual axis and the rotation angle of the eyeball depends on the luminance of an object to be observed at that time, and then, on the basis of the information thus obtained, the correction data are gathered.
However, in the foregoing calibration method, the photographer's pupil diameter does not change considerably at the time of the diaphragm of the photographing lens fully open or brought to the maximum step down. As a result, there is automatically a limit in precisely obtaining the exact data on the individual variations by depending on the variations of the pupil diameter.
Also, the correction data are gathered uniquely from the individual variation data for one time. Hence, if such individual variation data contain errors, there has been a problem that the correction data obtained therefrom also contain errors accordingly.